1. Field of the Ivention
The present invention relates to an active matrix color display screen without crossing of address line conductors and command column conductors. It is applicable to the display of fixed images, such as printed texts generated by word processors as well as to the display of animated images, such as TV images.
2. Description of Related Art
Active matrix liquid crystal color display screens are produced by associating two surfaces that encloses a liquid crystal.
FIG. 1 (Prior Art) depicts the elements disposed in a known manner on the first surface and constituting an elemental image point (pixel, in the International Language).
A thin film transistor 10 is connected at its base to a conducting line Li, at its collector to a conducting column Cj, and at its emitter to an electrode 12. The second surface is covered with colored electrodes forming a mosaic of filters of the three primary colors, red, green and blue, in the steps of the matrix.
Three principal types of arrangement of the mosaic of filters are currently utilized. They are depicted in FIG. 2 (Prior Art). One point of color image comprises three elemental image points of the colors red, blue and green. The elemental images points are symbolized by the squares; the colors attributed to them are noted: R:red, G:green, B:blue.
In FIG. 2A (Prior Art) there is represented the structure called "in bands." This configuration permits the stocking of three informations, R, G, B, simultaneously, but this arrangement of the filters is not visually favorable.
A structure of the "diagonal" type is depicted in FIG. 2B (Prior Art). This structure, more attractive visually than the preceding one, presents the disadvantage of a very complex addressing of the screen: a point of color image is distributed to two lines; the three colors are assigned to one and the same column.
A structure of the "triangle" type is depicted by FIG. 2C (Prior Art). The advantages concerning the visual comfort of this structure in relation to the two preceding ones are brought out in the article "Color pixel arrangement evaluation for LC-TV" by S. Tsuruta, K. Mitsuhashi and K. Noguchi appearing in the report of the 1985 international display research conference, p. 24.
FIG. 3 (Prior Art) depicts two known arrangements for putting the "triangle" structure into practice.
FIG. 3A (Prior Art) relates to the article "An amorphous-Si TFT addressed 3.2 in full color LCD" by F. Funada, Y. Takafuji, K. Yano, H. Take and M. Matsuura appearing in the SLD 86 digest report, p. 292.
This structure presents the disadvantage of elongating the length of the column conductors which must make zigzags between the electrodes corresponding to the image points, in such a manner as to be able to stagger the image points by a half step between two consecutive lines.
It is known, moreover, that the problems of fabrication become increasingly important with lengthening conductor runs; for example, the risks of short circuits and breaks are multiplied.
FIG. 3B (Prior Art) depicts a second possibility for putting into practice the "triangle" structure. This is described in the article "A high picture quality LC-TV using triangle trio-color dots" by Saito and his collaborators appearing in the report of the 1985 international display research conference, p. 27. This time, a color of an image point color puts in play two elemental image points of the same color. To each elemental image point there is assigned a thin film transistor. The problem posed by this proposed configuration is the large number of thin film transistors which makes addressing more complex, the production of the matrix more delicate, and which burdens the cost of fabrication.